The present invention is related to novel engine fuels which are more efficient and environmentally safer than conventional fossil fuels and nitromethane-based fuels. The inventive fuel compositions are suitable for igniting internal combustion engines, specifically 2-cycle, 4-cycle, and diesel engines, as well as jet propulsion engines.
2. Description of Related Art
Presently, race cars and dragsters having 4-cycle internal combustion engines use fuels containing as much as 90 to 95% nitromethane. Similarly, the smaller Hobby car and airplane engines (2-cycle and 4-cycle) use fuels containing from 5% to 40% nitromethane, over 50% methanol, and from about 18% to about 24% oil. While these fuels possess the necessary high levels of BTU's required to run these engines, nitromethane fuels are very dangerous as well as toxic to the environment. A conventional nitromethane (10%)/methanol (70%)/oil (20%) fuel, for example, has a vapor pressure of 196 mm Hg and thus, is very explosive. These fuels also leave relatively large amounts of liquid raw residue in the exhaust and are environmentally unsafe. In addition, the relatively large percentage of lubricating oil present in the fuel mixture, in particular conventional 2-cycle oils, also contributes to these emissions.
The small utility engines found in lawn and garden equipment such as lawnmowers, weedeaters, chain saws, grass blowers, and grass edgers as well as outboard motors and motorcycles, for example, are typically 2-cycle engines which generally use gasoline fuels containing a petroleum-based 2-cycle lubricating oil as a direct component of the fuel. Gasoline/oil fuels are used as alternatives to nitromethane fuels in the smaller Hobby engines, as well. From an environmental standpoint, the use of a gasoline/oil fuel in these 2-cycle engines has a more direct effect in producing emission pollutants than gasoline-only fuels used in most 4-cycle engines, primarily due to the additional oil component present in the fuel. [There are also special 4-cycle engines that, like 2-cycle engines, do not have a crankcase and thus require that a lubricating oil be directly added to the fuel.] For example, it was reported that many small utility engines produce up to 50 times the pollution of trucks per horsepower hour; that mowing the lawn for half an hour can produce as much smog as driving a new car 172 miles; and that using a chain saw for two hours gives off as many hydrocarbons as a car driven from coast-to-coast. [California Air Resources Board, statements in connection with a public hearing December 14, 1990 in San Francisco, Calif., "Small Engine Emissions," Technology Today, p.3, March 1991.] Consequently, there is a desire to reduce the amount of emissions produced from these small engines, either by fuel reformulation or the more costly redesign of present engines.
There have been various efforts to replace conventional fossil fuels typically used in 4-cycle internal combustion engines. In U.S. Pat. No. 4,818,250 to Whitworth, for example, a purified limonene fuel is disclosed for ignition of an internal combustion engine. This patent suggests that the limonene processed according to its teachings is a suitable additive for conventional fuels or may be used by itself as an alternative to such fuels. The limonene fuel is purified to remove contaminants and as much water as possible. The fuel is further processed to prevent gum formation, either by dehydrogenation of the limonene itself to remove the double bonds or by the addition of a suitable antioxidant. Since limonene has a relatively high flash point of about 113 to 124.degree. F., depending upon the grade used, it is believed that the fuel described by Whitworth is not capable, by itself, of igniting an engine unless the engine has a high voltage ignition. Large 4-cycle engines present in automobiles and trucks, for example, have high voltage constant electronic ignitions which are sufficient to ignite a fuel having such a high flash point. Conversely, 2-cycle engines generally require fuels having much lower flashpoints.
U.S. Pat. No. 4,818,250 further discloses other alternatives to conventional fuels, including U.S. Pat. No. 4,131,434 to Gonzalez, which is directed to a fuel additive for oil, diesel oil, and gasoline to improve fuel efficiency and reduce resulting air pollutants. Exemplary Gonzalez additives are aromatic and aliphatic hydrocarbon solvents with and without oxygenated functional groups, terpenes, and aromatic nitrogen containing compounds.
U.S. Pat. No. No. 2,402,863 to Zuidema et al., which is also discussed in the Whitworth patent, is directed to blended gasoline of improved stability and, more particularly, leaded gasoline containing up to about 10% alicyclic olefins which preferably contain a cyclohexane ring. Cyclic olefin is defined as an alicyclic hydrocarbon containing an olefin double bond in the ring (preferably no more than one). The alicyclic olefins are suggested to be available from terpenes or from synthesis such as partial dehydrogenation of naphthenes. A number of individual cyclic olefins are stated as being suitable, including, for example, terpenes such a dilimonene (citene) and d.sup.+ 1 limonene (dipentene).
It is therefore desireable to design an alternative fuel that is safer, environmentally cleaner, and as efficient, if not more efficient, than conventional fuels,